Bathurst burr

Xanthium spinosum
Herb
Alternate
Simple
White
Green
Green

An upright and much-branched herbaceous plant usually growing 30-100 cm tall. Its stems are armed with yellowish three-pronged spines (15-50 mm long) in the leaf forks. Its leaves are usually irregularly lobed, with dark green and shiny upper surfaces and pale green lower surfaces covered in downy hairsmale flowers are borne in dense clusters near the tips of the stems, while separate female flowers are borne in the leaf forks. Its stalkless 'burrs' (8-15 mm long) are covered in numerous small hooked spines (2-3 mm long).

Common names 
Also known as: Bathurst Burr, burrweed , spiny cockleburr, cat's eggs , clotbur, cocklebur, common cockleburr, spiny burweed, dagger cocklebur, Spanish thistle,
Family 
Asteraceae
Deciduous 
No
Flowering time 
Year Round
Native/Exotic 
Exotic
Origin 
Native to some parts of South America
Notifiable 
No
Council declaration 
SIL – Special Investigation List
Known distribution 

This species is very widely naturalised in Australia, particularly in the eastern half of the country. It is most common in New South Wales, the ACT, Queensland, Victoria and south-eastern South Australia, but is also scattered in the southern parts of the Northern Territory, in other parts of South Australia and in the southern and south-western parts of Western Australia. It is also occasionally naturalised in Tasmania. Bathurst burr (Xanthium spinosum) is also widely naturalised in other parts of the world, including Europe, the Azores, Africa, temperate Asia, Papua New Guinea, New Zealand, North America (i.e. the USA and Canada) and some parts of South America.

Habitat 

A weed of pastures, crops, waterways, grasslands, open woodlands, floodplains, waste areas, roadsides and disturbed sites in temperate, semi-arid, sub-tropical and sometimes also tropical and arid environments.

Habit 

An upright (i.e. erect) and much-branched short-lived (i.e. annual) herbaceous plant usually growing 30-100 cm tall, but occasionally reaching up to 1.2 m in height.

Impact and control methods 

Bathurst burr (Xanthium spinosum) is regarded as an environmental weed in Queensland, the Northern Territory, New South Wales, Victroia and South Australia. It was recently also listed as a priority environmental weed in five Natural Resource Management regions.

Stem and leaves 

The stems are greenish-yellow when young and are covered with fine hairs (i.e. finely pubescent). They are armed with spines that occur singly or in pairs at the base of each leaf stalk (i.e. in the leaf axils). These spines are usually three-pronged from near their bases and may appear to be several spines at first glance. They are yellow or greenish-white in colour with prongs 15-50 mm long. The alternately arranged leaves (2-10 cm long and 6-30 mm wide) are borne on stalks (i.e. petioles) up to 30 mm long. The lower leaves are usually irregularly three-lobed, or occasionally with five lobes, with the middle lobe much larger than the others. However, on upper leaves the side lobes may be insignificant or absent, thereby giving the leaf blade an elongated (i.e. lanceolate) shape. The leaf upper surfaces are dark green and shiny with prominent whitish-coloured veins, while their undersides are pale green or whitish in colour with a dense covering of downy hairs.

Flowers and fruits 

Separate male and female (i.e. unisexual) flower-heads are produced on different parts of the same plant (i.e. this species is monoecious). Male flower-heads consist of numerous tiny flowers (i.e. florets) that are arranged in dense rounded clusters. These male flower-heads are borne at the tips of the stems, and are yellowish or creamy-white in colour. The greenish-coloured female flower-heads are borne singly or in small clusters in the upper leaf forks (i.e. axils), usually below the male flower-heads. Flowering occurs from late spring through to early autumn, but is most abundant during summer. The fruit (8-15 mm long and 4-6 mm wide) is greenish when young, later becoming yellowish or straw-coloured, then eventually brownish as it matures. It is an oval-shaped (i.e. ellipsoid) 'burr' containing two seeds. These 'burrs' are stalkless (i.e. sessile), finely hairy, and covered in numerous small hooked spines (2-3 mm long). They also have two small, straight, spines or 'beaks' at the tip (1-2 mm long), which may be difficult to distinguish from the hooked spines. These fruit are mostly formed during late summer and autumn. The brown or black seeds (about 10 mm long) are flattened, and one of each pair is slightly larger than the other.

Reproduction and dispersal 

This species reproduces entirely by seed, contained in the 'burrs'.These 'burrs' are well adapted for dispersal, due to their hooked spines, and readily become attached to animals, clothing and vehicles. They may also be spread by water and in contaminated agricultural produce.

Similar species 

Bathurst burr (Xanthium spinosum) is similar to cockleburr (Xanthium ambrosioides) and the plants of the Noogoora burr complex (Xanthium strumarium sp. agg., which includes Xanthium occidentale, Xanthium orientale, Xanthium italicum and Xanthium cavanillesii ). These species can be distinguished by the following differences: Bathurst burr (Xanthium spinosum) has small to moderately sized leaves (2-10 cm long) that are relatively narrow (6-30 mm wide) and usually have three irregular lobes. These leaves have dark green upper surfaces and whitish coloured undersides. Its stems bear three-pronged spines near the leaf bases and its moderately-sized fruit (8-15 mm long) have 'beaks' that are small (1-2 mm long) or absent.cockleburr (Xanthium ambrosioides) has small leaves (2-4 cm long) that are very narrow (3-10 mm wide) and usually have three elongated lobes. Both leaf surfaces are finely hairy (i.e. pubescent) and greyish-green in colour. Its stems bear three-pronged spines near the leaf bases and its small fruit (4-8 mm long) usually do not have 'beaks' (occasionally one small 'beak' is present).the plants of the Noogoora burr complex (Xanthium strumarium sp. agg.) have relatively large leaves (up to 20 cm long) that are very broad (up to 18 cm across) and often have three or five lobes with irregularly toothed margins. Both leaf surfaces are green in colour and rough to the touch (i.e. scabrous). Their stems do not bear any spines and their relatively large fruit (7-30 mm long) are topped with two distinct 'beaks' (4-8 mm long).